The invention relates to a novel metallurgical process and apparatus for smelting or melting ferrous or other metal self-reducing agglomerate or metals.
In a conventional blast-furnace, a burden, comprising sized lump-ore, pellets, sinter and/or other classical agglomerates plus coke and limestone, is charged into the top of the furnace to form a continuously moving column or charge (i.e., a moving-bed). Atmospheric air, preheated in Cowpers up to 1200.degree. C., is blown through a row of tuyeres at the upper coke-filled portion of a furnace hearth to produce combustion and a reducing atmosphere due to the carbon monoxide formed by reaction of the air with carbon from the coke. This CO combines with oxygen from the iron oxide of the burden to reduce the oxides to metallic iron that then melts down and carbon saturates at the hearth, so as to produce pig iron.
The impurities, namely ore's gangue and coke ashes, form a less dense liquid slag floating over the surface of the molten pig iron.
The gases which flow countercurrently pre-heat and reduce the burden and leave the furnace through the top. These gases comprise mainly, CO, CO.sub.2, N.sub.2 and H.sub.2 O and are used at the Cowpers to preheat combustion air to the furnace and to other heating purposes within the plant.
The reduction is, therefore, carried out through CO generated from partial combustion of the coke. CO diffuses into the metal-bearing particles and a reduction, following the reaction MeO+CO.fwdarw.Me+CO.sub.2, takes place. The CO.sub.2 generated in this reaction then reacts into CO. These reactions require time and, thus, the need for a high residence time in order to attain high metallization of the charge. In typical blast-furnace operation, this residence time usually reaches 6 to 8 hours for a burden of agglomerates (pellets or sinter) or to 10 to 12 hours for a burden of sized lump ore.
Self-reducing agglomerates, which can be produced by currently known methods, present conditions much more favourable to reduction. A more intimate contact between the ore's oxides and finely divided charcoal or coal provide a lower reaction time since the time needed, in classical processes, for diffusion of CO from the furnace's atmosphere into the particles is not required because the reduction takes place rapidly inside the particles, again by the reactions: EQU 2 MeO+C.fwdarw.2 Me+CO.sub.2 EQU CO.sub.2 +C.fwdarw.2 CO EQU MeO+CO.fwdarw.Me+CO.sub.2
Unfortunately, in blast, cupola or other existing furnaces, the coke or other solid fuel is charged by the top to travel down and mix with, or settle over, the rest of the burden and, so, becomes exposed to and reacts countercurrently with the ascending CO.sub.2, following the reaction CO.sub.2 +C.fwdarw.2CO. This effect, known as "solution loss" according to the Boudouard principle, takes place on hot carbonaceous particle's surface. It counteracts CO.sub.2 formation within the furnace's atmosphere resulting in higher CO content of off-gases and, hence, in a higher consumption of coke, without any effective gain or advantage for the process. It prevents, in other words, reaching high CO.sub.2 /CO rates of top gases of blast, cupola, or other furnaces either when smelting ores or even when using self-reducing agglomerates.